1. Field of the Invention
The present invention relates generally to a viscous fluid type heat generator in which a viscous fluid is filled in a predetermined fluid containing chamber defined within a housing assembly and is subjected to a repeated shearing action by the rotation of a rotor element so as to generate heat which is in turn transmitted to a circulating heat exchanging fluid in a heat receiving chamber. The heat is carried by the heat exchanging fluid to a desired heated area, such as a passenger compartment in an automobile. More particularly, the present invention relates to a viscous fluid type heat generator in which the predetermined fluid containing chamber of the housing assembly is filled with a viscous fluid at filling rate suitable for generating heat of which the temperature is enough to be used with a heating system, while preventing a damage to an oil sealing device incorporated in the viscous fluid type heat generator.
2. Description of the Related Art
It is known to use a viscous fluid type heat generator as a supplementary heating device for motor vehicle heating systems. The supplementary heating device has a drive shaft operationally connected to and driven by a motor vehicle engine. The drive shaft is rotatably supported in a housing assembly which houses a rotor element drivingly connected to an inner end of the drive shaft. The housing assembly defines a heating chamber therein in which a predetermined amount of viscous fluid such as silicone oil is filled so that the viscous fluid is retained in spaces provided between the inner walls of the heat generating chamber and the outer surface of the rotor element. The filling rate of the viscous fluid for the heating chamber is generally set, for example, at higher than 80%, and the heating chamber is hermetically sealed by an oil seal element or a shaft seal element arranged within the heating chamber around the drive shaft so as to prevent leakage of the viscous fluid from the heating chamber.
The application of a fluid filling rate of 80% or more is based on the fact that the conventional viscous coupling device employing the same heat generating principle as the viscous fluid type heat generator has satisfactorily applied this filling rate. In the viscous coupling device, the viscous oil is used as a working medium, and an increase in the volume of the working medium due to frictional heat generation of the working medium is utilized for providing an adjustable fluid coupling between two clutch plates in order to transmit an adjusted torque from the input of the coupling device to the output thereof. Thus, in the viscous coupling device, it is often needed to provide a strong connection substantially corresponding to a direct connection between the two clutch plates so as to transmit a full torque from the input to the output of the coupling device, and accordingly, the filling rate of the viscous fluid must be designed and set at a value as high as possible.
Nevertheless, in the conventional viscous fluid type heat generator, heat generation occurs due to an application of a shearing action to the viscous fluid held between the inner walls of the heat chamber and the outer surfaces of the rotor element by the rotation of the rotor element. The heat generation of the viscous fluid causes an increase in the temperature of the viscous fluid, and therefore, expansion of volume of the viscous fluid as well as the air confined within the heat generating chamber occur. Therefore, an inner pressure prevailing within the heat generating chamber increases depending on an increase in the expansion of the volume of the viscous fluid and the air. When a volume occupied by the viscous fluid within the heat generating chamber is considerably larger than that occupied by the air within the heat generating chamber, namely, when the filling rate of the viscous fluid for the heat generating chamber is large, the inner pressure within the heat generating chamber may excessively increase beyond a predetermined durable pressure (the maximum permissible pressure) for the oil seal, due to a difference in the thermal expansion coefficients of the viscous fluid and the air. As a result, damage to the oil seal and leakage of the viscous fluid from the heat generating chamber might occur.